The present invention relates generally to the field of instantaneous frequency measurement (IFM) receivers with digital processing.
The conventional IFM receiver is a radio frequency receiver used primarily in electronic warfare. Its basic function is to measure the frequency of pulsed signals radiated from hostile radar. Generally, it may be said that IFM receivers measure the frequencies of incoming RF signals utilizing interferometric techniques by detecting the phase shift magnitudes produced in multiple, calibrated delay lines. For instance, the received RF signal is divided and simultaneously introduced into a non-delayed path and a delay line of known length. Since the phase differences between the delayed and non-delayed receiver paths are functions of the input signal frequency, conversion of the phase difference signals to video signals provides signals whose amplitudes are related to phase delay. These video signals typically take the form sin .omega..tau. or cos .omega..tau., where .omega. is the angular frequency of the processed input signal. The sin .omega..tau. and cos .omega..tau. signals are delivered to an encoding network which makes amplitude comparisons of the signals, determines the numerical value of .omega., and generates the digital frequency descriptive word.
An IFM receiver has many attractive features necessary for electronic warfare applications, such as small size, light weight, wide instantaneous bandwidth, and fine frequency resolution.
Typical IFM receivers are shown in U.S. Pat. Nos. 3,939,411 to James, and 4,336,541 and 4,426,648 to Tsui and Shaw. Other U.S. patents of interest are U.S. Pat. Nos. 4,021,804 to Dounce et al; 4,268,279 to Hines; 3,431,405 to Dawson; and 4,364,048 to Waters et al.